IMHO, with this being your first muzzle loader build/assembly, one of the Kibler kits would probably be you best investment. The locks of most flintlock manufacturers leave something to be desired. Some of the locks are generally good quality, though most could use a little tweaking, while some almost require a complete rebuild. The Kibler locks are the best I have seen, right out of the box. No tweaking or fiddling necessary. The kits are also the highest quality and practically snap together. And, there are multiple videos on the 'tube, including Kibler's, excellent, instructional videos. On top of that, there are quite a lot of people on this forum who can help walk you through any rough spots you might encounter.
As to which kit? What do you want to do with it? Hunt? Plink? Display on the wall? Shoot paper matches? Shoot steel? Have you thought about weight? Generally, the larger the bore diameter, considering the same, exterior, size of barrel, larger bores will be lighter to carry, for hunting. Smaller bores, are generally better for plinking and small game hunting, though with the same barrel diameter, as the large bores, the small bores will be heavier.
Larger bores use larger balls, which are more expensive, and they require heavier charges of powder to power those larger balls. Smaller bores, obviously, utilize smaller, lighter balls requiring less powder and less lead to feed them, which means less recoil and less expense. IMHO, 40 and 45 calibers are very pleasant to shoot, as are 50 and 54, with lighter powder charges, though the larger two, are more expensive to feed. And one last piece of advice, Flintlocks don't work reliably with black powder substitutes. It takes real black powder to make the flint lock function properly. And all of Kibler's kits are flintlocks, sporting 44 inch barrels, at this point in time.
Good luck with your new adventure.
